High dynamic range (“HDR”) image sensors are useful for many applications. In general, ordinary image sensors, including for example charge coupled device (“CCD”) and complementary metal oxide semiconductor (“CMOS”) image sensors, have a dynamic range of approximately 70 dB dynamic range. In comparison, the human eye has a dynamic range of up to approximately 100 dB. There are a variety of situations in which an image sensor having an increased dynamic range is beneficial. For example, image sensors having a dynamic range of more than 100 dB are needed in the automotive industry in order to handle different driving conditions, such as driving from a dark tunnel into bright sunlight. Indeed, many applications may require image sensors with at least 90 dB of dynamic range or more to accommodate a wide range of lighting situations, varying from low light conditions to bright light conditions.
One known approach for implementing HDR image sensors is to use a combination pixel. One sub-pixel can be used to sense bright light conditions while another sub-pixel can be used to sense low light conditions. However, this approach usually includes physical and electrical difference between different photodiodes in the sub-pixels. These differences can create challenges in processing the image signals generated from the different photodiodes. As a consequence, more complicated and less efficient read out and measuring electronics may need to be selected to read out the different photodiodes at the desired accuracy.